Related stories

The initial version supports only traditional username-password pairs, but in the future the technology will support multifactor authentication, in which people typically must type not just a password but also a numeric code from a smartphone. Google has supported dual-factor authentication with its user accounts for years, including for Chrome settings synchronization.

"We plan to release multifactor authentication (including dual-factor) in future versions of the product and will provide an update when we get closer to this," Mozilla spokesman Justin O'Kelly said.

Sync has become increasingly important to browsers as people have moved from using a single PC to using multiple computers, phones, and tablets. Sync helps not just with obvious things, like making sure a saved password works across multiple devices, but also functions like browser history, so a browser can do a better job of auto-completing addresses typed into the address bar.

Mozilla's username-password authentication for sync is now in the Nightly version of Firefox -- the raw builds made every night with the newest updates and least testing -- and will gradually spread to the more stable versions of Firefox.

"While the old version of Sync will continue to work, the latest version of Firefox doesn't support adding new devices to the old version of Sync. This means that you won't be able to sync with a new device," Mozilla explained.